Optical glass having a high refracting index and a high color dispersion

ABSTRACT

AN OPTICAL GLASS OF WHICH THE REFRACTIVE INDEX RANGES BETWEEN NE=1.77 AND NE=1.83, AND OF WHICH THE ABBE NUMBER RANGES BETWEEN VE=26 AND VE=23. THE GLASS CONSISTS ESSENTIALLY OF A GLASS FORMER OF SILICON DIOXIDE AND GERMANIUM DIOXIDE AND IN ADDITION THERETO A RELATIVELY HIGH PERCENTAGE OF TITANIUM DIOXIDE IS ADDED. OTHER INGREDIENTS PRESENT ARE THE OXIDES OF SODIUM AND POTASSIUM AS WELL AS THE OXIDES OF BORON AND LEAD. IN SPITE OF THE HIGH PERCENTAGE OF TITANIUM DIOXIDE THE GLASS IS ONLY FAINTLY COLORED.

United States Patent 3,703,389 OPTICAL GLASS HAVING A HIGH REFRACTING INDEX AND A HIGH COLOR DISPERSION Heinz Briimer, Hermannstein, and Norbert Meinert, Wetzlar, Germany, assignors to Ernst Lietz GmbH, Wetzlar,

Germany No Drawing. Filed Aug. 3, 1970, Ser. No. 60,630

Claims priority, application Germany, Aug. 14, 1969, P 19 41 374.2 Int. Cl. C03c 3/10, 3/30, 3/02 US. Cl. 106-47 Q 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The present invention relates to an optical glass having a high refractive index and a high color dispersion. The invented glass may be compared to the known flint glasses but has a considerably higher dispersion than the known glasses.

In the US. patent application Ser. No. 836,677 filed Apr. 4, 1969 and assigned to the same assignee as the present invention, flint glasses are disclosed which consist of a high percentage of titanium dioxide. The glasses have generally a higher color dispersion than the prior art flint and heavy flint glasses. It is a particular advantage of the glasses to have a considerably lower density than the known glasses, which fact becomes important especially with voluminous objectives.

The glasses disclosed in the above specified application consist essentially of 27 to 37% by wei ht of S102 and B 0 with the mol ratio of Si0 to B 0 ranging between 1.5 and 6, of 20 to 40% by weight of TiO and of 30 to 50% by weight of the oxides of a group consisting of the elements of lithium, sodium, potassium, rubidium, and cesium with the mol ratio of TiO to these alkali oxides ranging between 0.5 and 2. The quantity of SiO +B O in excess of 15% by weight of the total composition may be replaced by PbO and/or Sb O and the quantity of alkali oxides in excess of 20% by weight of the total batch composition may be replaced up to 25% by weight by the oxides chosen from a group including magnesium, calcium, strontium, barium, zinc, cadmium, and zirconium. These glasses have a power of refraction of 1.75, at the utmost, and an Abb number of about 27.

3,703,389 Patented Nov. 21, 1972 2 SUMMARY OF THE INVENTION It has now been discovered that an even higher power of refraction may be achieved in glasses containing a high percentage of TiO if SiO and GeO are used as the glass formers and the amount of those glass formers ranges from 28 to 40% by weight, with the percentage of GeO alone being about 10 to 20% by weight. The glasses consist further essentially of 14 to 40% by weight of TiO 12 to 30% by weight of the oxides of Na and K 10 to 30% by weight of PbO and Up to 5% by weight of B 0 These glasses may also contain 010% by weight of W0 and 0-15 by weight of Ta O The glasses have a refractive index of up to about 1.83 and Abb numbers of about 25. The high index is achieved by the reduction of the percentage of SiO and the percentage of the alkali oxides.

Further, the glasses are only slightly colored in spite of the high percentage of T102- This is probably due to the following circumstances. It is well known that TiO in an acidic solution tends to form suboxides which cause heavy coloring. This coloring may be obviated, according to the disclosure in the above mentioned patent application, by adding a large quantity of alkali oxides. Substituting the only faintly acidic germanium dioxide for the considerably more acidic silicon dioxide however, allows a substantial reduction of the alkali oxides without running the risk of titanium dioxide forming suboxides. Like the glasses disclosed in the above mentioned patent application, the glasses according to the invention have also the advantage that they are substantially lighter in weight than the flint and heavy flint glasses presently available on the market.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Melt No.

Prloi art Mol Percent by wt.

Mol Percent percent bywt.

Percent by wt. percent TABLE 2 Melt N0.

M01 percent Percent by wt.

Percent Percent b by wt.

TABLE 3 Melt No.

Percent Mel Percent M01 Percent Mol Percent Mol Percent Mol by wt. percent by wt. percent by wt. percent by wt. percent by wt. percent.

5102 17. 90 25. 78 17. 25. 94 17. 90 27. 15 17. 90 28. 48 12. 90 21. 25 B203 1. 90 2. 44 1. 06 2. 46 1. 96 2. 67 1. 00 2. 69 1. 90 2. 70 IbO 20. 02 7. 99 20. 62 8. 20. 62 8. 42 83 0. 11 T: 24. 90 20.96 24.00 27. 13 10 90 22 70 18. 45 G002 15.00 12. 41 15.00 12 40 00 13 O7 18. NnzO 10.62 23.21 16.62 23.35 16 62 21 11 Example of glass production from a total of the oxides of tungsten and tantalum in the following 1 kg. raw materlal quantities:

The various chemical components of a batch are W03 0-10 percent by p thoroughly mixed and then placed in portions in a plati- T3205 Percent by Hum crufible P F P about 11505 The melt is 3. The optical glass of claim 1, wherein B 0 is 1.96 homogenized by stirring at a temperature of about 1250 percent by Weight C. When the melt is completely free from bubbles the 4' The optical glass of claim 2 wherein W03 is about temperature 1s lowered to about 1100 C. and maintained 3 Percent by weight for 15 minutes under continual stirring. Thereafter, the

melt is cooled to 900 C. and then poured into a pre- References Cited heated steel mold.

What is claimed UNITED STATES PATENTS 1. An optical glass having an index of refraction n of 3, 9/ 1970 Bro e et a1 106-47 Q between about 1.77 and 1.83, and a high color dispersion ,60 ,817 11/ 1926 Dennis 106-53 value (an Abb number v between about 23 and 26) 3,486,9 5 12/1969 Bromer et al 106-47 Q consisting essentially of: FOREIGN PATENTS 28-40 percent by weight of a mixture of SiO- and GeO 1,037,932 8/1956 Great Britain 10 3 wherein GeO is about 10-20 percent by weight, 14-40 percent by weight of T10 JAMES E. POER, Primary Examiner 12-30 percent by weight of the oxides of Na and K, 10 3O Percent by weight of Pbo and M. L. BELL, Ass1stant Examiner up to 5 percent by weight of B 0 U S C1 X R 2. The optical glass of claim 1 and further containing 106-53 

